Amid increasing reports of children nationwide plagued with polio-like paralysis over the past four years, some experts suggest that a virus may be the cause, but federal health officials are not so sure.

Since the onset of the first AFM outbreak in 2014, which paralyzed a dozen children, doctors and the Centers for Disease Control and Prevention (CDC) have been baffled by the true cause of the disease.

However, according to a report by NBC News, researchers from a number of children’s hospitals and former CDC officials nationwide formed a loose network to investigate the problem and say they now believe that enterovirus D68 is the cause of the child paralysis cases.

Experiments researchers have conducted show the virus can invade nerve tissue, including the spine, and affect motor function. There is also evidence of genetic changes in the virus itself.

Acute flaccid myelitis has a sudden onset, directly effecting the spine and nervous system. While the virus is often harmless to people impacted, in some cases it causes disabling paralysis similar to polio, primarily affecting children. These serious issues often begin with a cold, and progress to weakening of the limbs or paralysis.

While the CDC indicates that children with acute flaccid myelitis do not consistently test positive for the D68 virus or suffer paralysis, many researchers disagree with the recent conclusions, and maintain that evidence points to D68 as the likely cause. They indicate the virus may have changed in recent years, making paralysis more likely.

Association Between D68 Outbreaks and AFM Outbreaks

Since 2014, there has been an increase in the number of cases of D68 surrounding outbreaks of acute flaccid myelitis. Every time D68 infections occur there is also an increase in AFM cases. But the virus is not confirmed in every case, which is why the CDC is reluctant to point to D68 as the true cause.

State health departments across the country reported 155 possible cases of acute flaccid myelitis this year alone. Yet, only 62 of those cases have been confirmed positive for the D68 virus.

A similar outbreak occurred in New York in 2014 and 2016 resulting in 160 confirmed cases of the illness. Similarly, European researchers reported 29 cases of D68 in children and adults with AFM in 2016.

The CDC still cannot definitively connect the evidence to show D68 can account for an increase in cases of acute flaccid myelitis.

Better surveillance is needed to determine if other viruses are causing the illness or if D68 is the true cause, experts say. Researchers are urging doctors to begin testing much faster, especially among children who begin showing signs of weakness or paralysis.

The faster a test can be completed, the easier it is to find the virus. However, the longer doctors wait after symptom onset to test for the virus, the harder it is to detect the virus and may account for the discrepancy.

The virus can cause damage to the nervous system, then disappear when the immune response kicks in to fight the virus, indicate researchers.

Researchers also speculate the paralysis could be an immune response to the infection, not just a side effect of the virus. In some cases, patients may have a genetic predisposition to paralysis making them more susceptible.

Regardless of the mechanism, researchers warn it is imperative to test early at the first signs of the illness.

Researchers are also investigating the long term effects of the illness. In previous reports, some patients diagnosed with acute flaccid myelitis have recovered quickly, whereas others have been found to continue to suffer from paralysis requiring ongoing care.

The CDC’s investigation will require help from state and local health departments to send information about suspected cases, verify clinical information of suspected cases, and testing specimens including stools, blood, and cerebrospinal fluid.